That doesn't mean that one mistake is going to destroy your brand's credibility -- we all make mistakes, but consistently poor grammar can make your brand look unprofessional and careless.

Brands today don't have to follow every grammatical rule in the book (it's better to speak the language of your buyer persona than that of a college English professor), but there's also a difference between using poor grammar on purpose and not knowing any better.

And believe me, everyone can spot the difference.

Here are 15 examples of grammar mistakes that everyone seemed to notice, except the brands themselves.

1. Old Navy

It's amazing to me that this shirt design made it all the way to a public release before anyone realized the apostrophe was missing. Old Navy ended up replacing the shirt in all of their stores and online.

2. Creative Kids Software

I'm not sure which retailer this is, but I'm just glad they're the ones selling educational software and not actually creating it.

3. Mitt Romney

If you're applying for a job, and you misspell the name of the company you want to work for, you most likely won't get that job.

4. Cincinnati State

It's extra embarrassing when a university makes grammatical mistakes. At least the billboard was advertising a science degree and not writing or literature.

5. Miller Beer

The only excuse I can come up with for the team behind this billboard is that they might have sampled too much of the product when brainstorming this groundbreaking slogan for their client.

6. Stratford Hall

Let's just hope that they uphold a higher standard to detail for their customers' cards than they do for their own ads.

7. Kmart

Stay in school kids.

8. Reebok

Reebok's right. Not everything needs to be done in a New York minute, especially not editing.

9. John McCain

I'm starting to notice a correlation between grammatical errors and presidential candidates that didn't win.

There's gotta be a lesson in there somewhere.

10. Stella Artois

I'm guessing that price is less than what it costs to hire an editor.

11. H&M

Since this is H&M, I'm going to give them the benefit of the doubt and assume the genius behind this design was trying to be ironic.